I think I may have made a mistake when asking this girl out. How do I fix it?

Hello, I have been talking to this girl for over a month now, and yesterday I asked her out. She told me she would have to find out if she could get time off work next, I said "okay cool" and we continued on talking for a bit without any awkwardness. I was just thinking last night that what she said may have just been an excuse, but I'm not sure. I do know she works odd hours, but a old friend told me she has been like this with other guys in the past. I'm not sure what to do. I just text her there and she read it, but there hasn't been a reply. Maybe I was being too quick? I wouldn't know this is the first time I have ever asking a girl out. If I made a mistake I'd like to correct it. What do I say to her to do this?Thanks